U.S. patent application number 10/412645 was filed with the patent office on 2005-01-13 for biometric sensor apparatus and methods.
This patent application is currently assigned to STMicroelectronics Ltd.. Invention is credited to Dennis, Carl.
Application Number | 20050008197 10/412645 |
Document ID | / |
Family ID | 28051848 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050008197 |
Kind Code |
A1 |
Dennis, Carl |
January 13, 2005 |
Biometric sensor apparatus and methods
Abstract
The optical biometric sensor apparatus and methods for analyzing
images of biometric features such as fingerprints are adapted to
distinguish between live body members and inanimate objects, and to
detect spoofing devices applied to live body members. Live body
members are detected by transmitting IR light from a first IR light
source through an object to an image sensor. The IR transmission
characteristics of a live body member vary with the human
heartbeat, and multiple images are analyzed to verify whether the
object is a genuine live body member. A visible light source
illuminates the object for obtaining a detailed image from the
sensor for conventional biometric analysis. Transmitted IR images
and reflected visible light images are also processed to detect the
presence of spoofing devices applied to live body members. Multiple
IR and visible light sources of different wavelengths may be used
for this purpose.
Inventors: |
Dennis, Carl; (Edinburgh,
GB) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
STMicroelectronics Ltd.
Buckinghamshire
GB
|
Family ID: |
28051848 |
Appl. No.: |
10/412645 |
Filed: |
April 11, 2003 |
Current U.S.
Class: |
382/115 |
Current CPC
Class: |
G06K 9/00013 20130101;
G06K 9/00114 20130101 |
Class at
Publication: |
382/115 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2002 |
EP |
02252601.6 |
Claims
That which is claimed is:
1. Biometric sensor apparatus comprising: a translucent platen
having a first side against which a body member to be analyzed by
the apparatus is placed, in use of the apparatus, and a second
side; at least one IR light source located on the first side of the
platen for transmitting light through the body member and the
platen to the second side of the platen; an optical image sensor
located on the second side of the platen for detecting light
transmitted through the body member and the platen.
2. The apparatus of claim 1, further including at least one visible
light source located on the second side of the platen and arranged
such that light from the visible light source is transmitted
through the platen and reflected by the body member for detection
by the image sensor.
3. The apparatus of claim 1 or claim 2, further including data
storage and processing means for storing and processing signals
output from the image sensor.
4. The apparatus of claim 3, wherein said data storage and
processing means is adapted to store and process a plurality of
images obtained from the image sensor in response to IR light
transmitted from the IR light source through an object placed on
the platen so as to determine whether the object is a live body
member.
5. The apparatus of claim 4, wherein the data processing means is
adapted to analyze relative intensities of said plurality of images
to determine whether variations in those intensities are consistent
with characteristics of a human heartbeat.
6. The apparatus of any one of claims 3 to 5 when dependent on
claim 2, wherein the data processing means is adapted to process at
least one image obtained from the image sensor in response to IR
light transmitted from the or each IR light source through a live
body member placed on the platen and at least one image obtained
from the image sensor in response to visible light from the or each
visible light source reflected from the live body member placed on
the platen so as to determine the presence or absence of a spoofing
device applied to the live body member.
7. The apparatus of any preceding claim, including at least two IR
light sources for transmitting IR light through the body member,
each of the IR light sources emitting IR light in a waveband that
is distinguishable from the waveband of any other of the IR light
sources.
8. The apparatus of any preceding claim, wherein the or each IR
light source emits IR light in a waveband in the range 700 nm to
1100 nm.
9. The apparatus of any preceding claim, including a first IR light
source that emits IR light with a wavelength of 850 nm.
10. The apparatus of claim 9, including a second IR light source
that emits IR light with a wavelength of 750 nm.
11. The apparatus of any preceding claim, including at least two
visible light sources for reflecting visible light from the body
member, each of the visible light sources emitting visible light in
a waveband that is distinguishable from the waveband of any other
of the visible light sources.
12. The apparatus of any preceding claim, wherein the image sensor
is a CMOS image sensor.
13. A method for determining whether an object presented to a
biometric sensor device is a live body member, comprising:
transmitting IR light from an IR light source through the object;
detecting IR light transmitted through the object using an optical
image sensor; obtaining a plurality of images from the image sensor
in response to IR light transmitted from the IR light source
through the object; and processing said images to determine whether
the object possesses predetermined characteristics of a live body
member.
14. The method of claim 13, wherein the step of processing said
images comprises analyzing relative intensities of said plurality
of images to determine whether variations in those intensities are
consistent with characteristics of a human heartbeat.
15. A method of determining whether a live body member presented to
a biometric sensor device has a spoofing device applied thereto,
comprising: transmitting IR light from at least one IR light source
through the body member; detecting IR light transmitted through the
body member using an optical image sensor; obtaining at least one
image from the image sensor in response to IR light transmitted
from the IR light source through the body member; reflecting
visible light from at least one visible light source from the body
member; detecting visible light reflected from the body member
using the optical image sensor; obtaining at least one image from
the image sensor in response to visible light from the visible
light source reflected from the body member; and processing said
images so as to determine the presence or absence of a spoofing
device applied to the body member.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to biometric sensors and
methods. More particularly, the invention relates to devices and
methods using optical imaging of fingerprints, handprints or the
like to verify a person's identity, and which are resistant to
"spoofing". The invention is particularly concerned with
determining whether a finger, hand or the like presented to a
biometric imaging device is a live finger, hand etc.
BACKGROUND OF THE INVENTION
[0002] To be secure, identification systems need to be robust
against fraud; i.e. to ensure that one person cannot pass
themselves off as another person.
[0003] The field of biometrics relates to the statistical analysis
of physiological characteristics. For the purposes of
identification for security or other purposes, features such as
fingerprints or retinal scans can be used to uniquely identify
individuals. Every person has a unique set of fingerprints, and
this provides a basis for identification. An image of a fingerprint
can be taken and analyzed to see if it matches a recorded sample of
the user's fingerprints. This is done by analyzing a number of
details, or "minutiae" of the fingerprint. The greater the number
of minutiae that are analyzed, the less are the chances of
incorrectly identifying an individual.
[0004] However, a biometric identification system that relies
solely on mathematical analysis of simple optical images can be
easily spoofed, as a copy of the pattern of a fingerprint can be
easily made and presented to a reader device. Accordingly, systems
have been developed to identify whether the finger to be identified
is indeed a three-dimensional finger, rather than just a photocopy
or the like. Such a system is disclosed in U.S. Pat. No. 6,292,576
(Brownlee). A finger to be identified is placed on a platen and is
illuminated by two light sources. The first light source
illuminates the finger from directly below the finger, and a
positive image is obtained, and the second light source is
positioned at an angle greater than the critical angle so that the
beam is subject to frustrated total internal reflection (FTIR) to
obtain a negative image. The images can then be added, and if a
true finger is present, the two images will cancel each other out,
whereas if a spoof is present, the images from the two light
sources will reinforce each other.
[0005] Such methods using FTIR are well explained in U.S. Pat. No.
6,292,576 and are well known in the art. However, such methods can
still be spoofed, for example by rubber models of a finger.
Therefore, besides analyzing the details of a fingerprint, it is
desirable for a biometric identification system to verify the
presence of a live finger (or other relevant body member).
International Patent Publication Number WO 01/24700 gives some
examples of such techniques. In this case, the ridges of the
fingerprint act as one plate of a capacitor. Properties of a live
finger such as perspiration, warmth, and pressure, mean that the
conductivity of the ridges will change, thus affecting the
capacitance. Thus, a finger can be tested with solid state
capacitive sensors to see if it has the electrostatic properties
that are characteristic of a live finger.
[0006] Such methods and other examples of biometric identification
are well known in the art. However, they are expensive to
implement. There is a need for a live finger detection apparatus
that is robust against spoofing and that can be easily
manufactured, installed and used.
SUMMARY OF THE INVENTION
[0007] The present invention provides a biometric sensor apparatus
and methods using optical imaging of a body member such as a
finger, hand or palm, and adapted to identify a live body member.
As used herein, "optical image sensors" means sensors that are
responsive to electromagnetic radiation at least in the visible and
infra red (IR) or near-IR spectra. Hereafter, references to IR
include near-IR.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will now be described, by way of
example only, with reference to the accompanying drawing, in
which:
[0009] FIG. 1 is a block diagram schematically illustrating an
embodiment of a biometric sensor apparatus in accordance with the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] The invention will be described in relation to systems for
biometric identification based on fingerprints, but is also
applicable to identification based on unique characteristics of
other body members, particularly hand or palm prints.
[0011] As shown in FIG. 1, a preferred embodiment of a biometric
identification system in accordance with the invention is adapted
to read and analyze a fingerprint of a fingertip 10 placed in
contact with a translucent platen 12. It will be evident to those
skilled in the art that in this context the term "translucent"
includes the case where the platen 12 is in fact transparent. At
least a first and preferably first and second IR illumination
sources 14 and 16, suitably light emitting diodes (LEDs), are
arranged above the platen 12 to transmit light of selected
frequencies in the IR band through the fingertip 10 and platen 12.
At least a first visible illumination source 18, again suitably an
LED, is arranged below the platen 12 to transmit visible light
through the platen 12 for reflection from the fingertip 10 back
through the platen 12.
[0012] An optical image sensor 20, suitably a solid state image
sensor such as a CCD or, most preferably, a CMOS device, is
arranged below the platen 12 to receive transmitted light from the
first and second IR LEDs 14 and 16 and reflected light from the
visible LED 18. For the purposes of the present invention, the
image sensor 20 is suitably a monochromatic (grayscale) sensor,
rather than a color sensor. One or more lenses or the like (not
shown) may be provided between the platen 12 and the sensor 20 as
required. The sensor 20 is connected to data storage and processing
means 22 for storing and processing signals received from the
sensor 20.
[0013] As shall be described in more detail below, the first IR LED
14 is used in combination with the sensor 20 for live finger
detection in accordance with the invention. The visible LED 18 is
used in combination with the sensor 20 for obtaining a detailed
image of a fingerprint for biometric identification, in a manner
that is well known in the art. In accordance with further aspects
of the invention, the first and/or second IR LEDs 14 and 16 are
used in combination with the visible LED 18 and sensor 20 to
provide additional protection against spoofing; e.g. by a fake
fingerprint applied to a live fingertip.
[0014] As noted above, the first IR LED 14 is used in determining
whether the fingertip 10 is a live finger, and not a spoofing
device such as an imitation finger. For this purpose, the invention
employs principles used in the medical field of pulse oximetry. The
tissues of a body member such as a fingertip are almost transparent
to IR light. However, blood absorbs IR light. This phenomenon is
exploited in pulse oximetry for a variety of clinical purposes,
including the detection of heart rate, the sinus rhythm of the
heart beat, the presence of blood vessels and the percentage of
dissolved oxygen in the bloodstream. The present invention applies
such techniques in a simplified form for biometric purposes, to
detect characteristics of a beating human heart that are present in
a live finger but absent in a spoofing device.
[0015] During the pulsatile phase of a heart beat, blood flows
through the arteries of a finger, causing them to dilate, while
other parts of the finger, such as the tissue and bone, and the
venous blood vessels do not change in diameter. Therefore, the
intensity of transmitted light will vary between the pulsatile
phase and non-pulsatile phase as a result of the blood flow. This
difference in intensity of transmitted light can form the basis for
forming an image of the blood vessels in a finger and for gathering
information about the blood flow in these vessels. The intensity
will vary according to the Lambert-Beer law, which states that the
intensity of a beam of monochromatic radiation varies exponentially
with the medium's thickness.
[0016] A pulse oximeter is designed to calculate the respective
levels of various types of hemoglobin in the blood, based on the
different absorption coefficients of oxygenated and de-oxygenated
blood. However, the present invention is not concerned with making
such detailed measurements, as it merely needs to detect the
presence of a live finger.
[0017] As shown in FIG. 1, a finger 10 to be identified is placed
on a transparent platen 12. First IR LED 14 transmits light at a
selected IR wavelength. The choice of wavelength is limited by the
transmission characteristics of the fingertip and the sensitivity
of the sensor 20. The minimum wavelength that is usefully
transmitted through a fingertip is about 700 nm. The maximum
wavelength detectable by a conventional optical CMOS sensor is
about 1100 nm. Conventional, nominally monochromatic LEDs typically
have a bandwidth of the order of 20 to 50 nm. In this preferred
embodiment, a monochromatic LED having a nominal wavelength of 850
nm is suitable, but LEDs having nominal wavelengths up to 1100 nm
may be used. Higher wavelengths could be used with specialized
sensors. However, for the purposes of the present invention it is
preferable to use a wavelength that is detectable by a conventional
image sensor, which is also employed for obtaining the detailed
fingerprint image for biometric identification.
[0018] For the purpose of live finger detection, at least two
transmitted IR images are required for comparison with one another,
to detect a pulse. For practical purposes it desirable to capture a
larger number of images over a period of time determined by typical
human heart rates, so as to obtain sufficient data to verify the
existence of a genuine human pulse waveform. In the preferred
embodiment, the pulse data obtained from the IR images are analyzed
to make sure that the waveform corresponds to a typical sinus
waveform indicative of a human heart beat, and then the period of
the heart beat is measured, to see if it falls into a predetermined
range of typical human heart beats. To accomplish this, the data
must be sampled at an adequate rate, preferably of the order of
five to ten times the Nyquist frequency for the highest frequency
component of a typical heart beat. Therefore, the sensor 20 might
be required to process hundreds or thousands of frames of
information per second.
[0019] A typical image sensor 20 for obtaining a detailed
fingerprint image for biometric identification may have a pixel
array typically comprising anything between 50,000 and 300,000
pixels. However, for the purposes of live finger detection in
accordance with the present invention, it is only necessary to
capture and process data from a small proportion of these pixels.
For example, data may be collected from a window of about
sixty-four pixels for each frame. The data value measured for each
frame could be the average of the data value for each of the
sixty-four pixels. This facilitates the high sampling rate referred
to above.
[0020] The live finger detection described thus far protects an
optical fingerprint reader against spoofing by inanimate objects or
images, in accordance with one aspect of the invention. The visible
LED 18 and sensor 20 are used firstly to obtain detailed
fingerprint images for biometric identification in a manner that is
well known in the art and which will not be described in detail
herein. In accordance with a further aspect of the invention, the
visible LED 18 is also used in combination with the first and/or
second IR LEDs 14 and 16 and the sensor 20 to provide further
protection against spoofing by imitation fingerprints applied to
live fingertips, as shall now be described.
[0021] In accordance with this further aspect of the invention,
images obtained by one or more IR light sources in transmission
mode (through the fingertip) are compared with images obtained by
one or more visible light sources in reflection mode (from the
fingertip) to determine whether they are consistent with a genuine
finger or whether they indicate the presence of a spoofing
device.
[0022] In a similar manner to the above-described embodiment of the
invention, data may be collected from a window of about sixty-four
pixels for each frame, in order to facilitate the high sampling
rate referred to above. A frame of data, or several frames averaged
to reduce noise, is acquired under each illuminant. The human
finger transmits and reflects light in well recognized proportions,
giving it a particular "color" defined by the intensity of the
measured pixels. A spoofing device that is not itself made of flesh
will not have this characteristic color.
[0023] Where multiple IR light sources are used, it is preferred
that these should emit light in non-overlapping IR wavebands,
within the limits discussed above for the first IR LED 14. However,
partially overlapping IR wavebands may be used, as long as the two
signals are distinguishable. Similarly, where multiple visible
light sources are used, these should emit light in non-overlapping
visible wavebands (typically within the range 380-780 nm). However,
partially overlapping wavebands could be used as long as they are
distinguishable.
[0024] The use of more IR and/or visible light sources provides
more data at different wavelengths, improving the reliability of
the system. However, it is desirable to minimize the number of
light sources to minimize the cost and complexity of the system. As
a minimum, one IR and one visible light source are required to
provide live finger detection and additional anti-spoofing
functions together with biometric identification. The addition of a
second IR source 16 improves robustness at minimal additional cost.
Where the first IR LED has a wavelength of 850 nm, as described
above, the second IR LED 16 might suitably have a wavelength of 750
nm.
[0025] In use, the system would preferably perform live finger
detection as a first step. If this test is passed, the secondary
anti-spoofing test would be performed. Only once both these tests
had been passed would the system perform full biometric analysis of
the detailed fingerprint image. The data storage and processing
means 22 may comprise any suitable types of memory and processor,
located locally to or remote from the light sources and sensor. If
they are located locally, they may be integrated into the same IC
as the sensor 20 or be provided on a PCB shared with the
sensor.
[0026] Improvements and modifications may be incorporated without
departing from the scope of the invention as defined in the
appended claims.
* * * * *